People who live in urban areas tend to have higher blood pressure, according to a new study that pins the blame on particulate air pollution.

Researchers examined data from an ongoing study of 5,000 people that focused on the development of heart disease. They analyzed the effects of air pollution exposure — pollution ranging from auto exhaust and power plants to roadway dust — on blood pressure between 2000 and 2003.

The findings are to be announced at a meeting of the American Thoracic Society being held in New Orleans this week.

"This finding points out that air pollution does not only trigger life threatening events like heart attacks and strokes, but that it may also influence the underlying processes, which lead to chronic cardiovascular diseases," said Dr. Barbara Hoffman of the University of Duisburg-Essen and senior author of the study. "It is therefore necessary to further our attempts to prevent chronic exposure to high air pollution as much as possible."

High blood pressure increases the risk for atherosclerosis, a hardening of the arteries, which leads to cardiovascular diseases like heart attacks and strokes. Previous work had shown that daily increases in air pollution can raise blood pressure, but little was known about long-term effects.

"Our results might explain why people who live in more polluted areas are at a higher risk to suffer and die from these diseases," Hoffman said.

The results held even after other factors that influence blood pressure were taken into account, including age, gender, smoking, weight and even local noise.